Cloning and Analysis of the β-Lactamase Gene from ε-Poly-L-lysine-Producing Actinomycete Streptomyces albulus IFO 14147

抄録

Streptomyces albulus IFO 14147 produces ε-poly-L-lysine, which exhibits antimicrobial activity. It is necessary for its molecular breeding to develop host-vector systems. We recently found a novel cryptic plasmid, pNO 33, in this strain. As part of a search for a selectable marker gene for pNO 33, we report here the isolation and analysis of the β-lactamase gene of this strain, which can grow on ampicillin-containing plates. It was shown that the β-lactamase production in S. albulus was induced by ampicillin. By introducing a genomic library of S. albulus into Escherichia coli, a 3.6-kbp fragment was identified as the region involved in ampicillin resistance. It contained three open reading frames, all of which are highly homologous to the β-lactamase (the blaL product) and its regulatory proteins (the blaA and blaB products) of S. cacaoi. The growth phenotypes and enzyme assaying of E. coli and S. lividans showed that the blaL homologue (blaSa) encodes a β-lactamase required for ampicillin resistance. The β-lactamse gene can be utilized as a selectable marker in a cloning vector of S. albulus. However, the β-lactamase activity was decreased in E. coli and repressed in S. lividans by the blaA and blaB homologues (blaASa and blaBSa). It appears as if the blaASa product is a repressor of blaSa instead of an activator as in S. cacaoi.